1. Field of the Invention
The present invention relates to an optical pick-up actuator which can automatically compensate a tilt resulting from a deflection or mechanical run-out of a disk.
2. Description of the Related Art
In pace with the development of disk media capable of optically recording information and reproducing the recorded information, diverse products have been developed in association with optical pick-up devices adapted to read information recorded on disks or to record information on disks.
In an optical recording/reproducing system for optically recording and reproducing information, an object lens driving unit configured to allow an optical spot to follow the surface vibrations and eccentricity of a disk is used, along with the optical system of a pick-up device, in order to achieve desired focusing and tracking operations.
This object lens driving unit is called an “optical pick-up actuator”. The current tendency of designs and developments associated with such an optical pick-up actuator is toward those suitable for high-density disks.
Generally, an optical pick-up actuator serves to move a bobbin including an object lens to maintain a desired relative positional relation between the object lens and a disk. The optical pick-up actuator also serves to trace tracks of the disk in order to read information recorded on the disk or to record information on the disk. Such an optical pick-up actuator is driven in accordance with a moving coil system utilizing a magnetic field created by permanent magnets, thereby moving the object lens to a desired position. The moving part of the optical pick-up actuator is designed to be supported by supporting members (suspension wires) having a desired rigidity and attenuation characteristics so that it has desired frequency characteristics. The moving part conducts translational motions in focusing and tracking directions perpendicular to each other. In order to reduce errors involved in optical signals, the moving part should be driven without generating unnecessary vibrations such as rotation or torsion.
Such an optical pick-up actuator includes a lens holder adapted to hold an object lens. The lens holder should be configured to move upward, downward, left and right directions, for desired focusing and tracking operations of the object lens. This driving unit also includes a coil arranged in a magnetic space defined by magnets and a magnetic body, so that it utilizes a Lorentz force according to the Fleming's left-hand law.
FIGS. 1A and 1B are schematic views respectively illustrating the configuration of a conventional optical pick-up actuator.
Referring to FIGS. 1A and 1B, the conventional optical pick-up actuator includes a lens holder 102 adapted to hold an object lens 101, magnets 103, yokes 104, a tracking coil 105, a focusing coil 106, a plurality of wire springs 107, fixed printed circuit boards (PCBs) 108, and a frame 109.
In the optical pick-up actuator illustrated in FIGS. 1A and 1B, the lens holder 102 mounted with the object lens 101 is movable in accordance with the function of the wire springs 107. The object lens 101 is centrally attached to the lens holder 102. The focusing coil 106 is wound around the lens holder 102. The tracking coil 105, which has a rectangular wound coil shape, is attached to the upper surface of the focusing coil 106. The fixed PCBs 108 are fixedly mounted to opposite side surfaces of the lens holder 102, respectively. The yokes 104 are symmetrically arranged at opposite sides of the object lens 101, respectively. The magnets 103 are arranged to apply magnetic flux to the tracking coil 105 and focusing coil 106, thereby causing the tracking coil 105 and focusing coil 106 to generate electromagnetic forces, respectively.
The yokes 104 are installed to be integral with a pick-up base, using an integral attachment means.
The frame 109 is arranged at one edge of the optical pick-up actuator. A main PCB not shown is fixedly mounted to the frame 109 by means of set screws. Each of the wire springs 107 is coupled to the frame 109 at one end thereof. Typically, four wire springs 107 are coupled to the frame 109. The other end of each wire spring 107, which is coupled to the frame 109 at one end thereof, is connected to an associated one of the fixed PCBs 108 attached to the lens holder 102. In accordance with such an arrangement, the lens holder 102 is maintained in a suspended state by the wire springs 107.
Now, the operation of the conventional optical pick-up actuator having the above mentioned configuration will be described.
When current is applied to the focusing coil 106 under the influence of a magnetic field, an electromagnetic force is generated from the focusing coil 106. This electromagnetic force serves to drive the moving part of the optical pick-up actuator, that is, a lens holder assembly, in upward and downward directions, that is, focusing directions. When current is applied to the tracking coil 105 in the same fashion as mentioned above, the moving part of the optical pick-up actuator moves in left and right directions, that is, tracking directions.
In accordance with such focusing and tracking operations, a laser beam emitted from the object lens 101 can always be focused onto the reflection surface of the disk recorded with signals (pits) at a desired focusing depth (focusing operation) while tracing the tracks of the disk (tracking operation).
Recently, requirements of recording and reproduction of large-quantity data have been increased. In pace with such requirements, data recording and reproducing media, that is, optical disks, have been developed to have a higher density. In order to record information on such a high-density disk or to read the recorded information, the size of the laser beam focused onto the disk should be correspondingly reduced. To this end, it is necessary to use a laser with a reduced wavelength λ and an object lens with a reduced numerical aperture NA. Here, the diameter of a focused laser beam, D, can be expressed by “D=0.82×λ/NA”.
Meanwhile, the tilt margin of a drive control system for optical disks depends on the characteristics of elements included in an optical system used. Typically, the tilt margin should meet the condition “tilt margin∝λ/NA3”.
Thus, tilt compensation is strongly required in drive systems used for data recording and reproduction in association with high-density disks. In particular, tilt components resulting from a deflection or mechanical run-out of a disk may adversely affect the control system. In drive systems used for data recording and reproduction in association with high-density disks, accordingly, it is necessary to use an optical pick-up actuator capable of tracing the tilt component of the disk in order to realize a stable servo.